This invention relates generally to a flat panel display and, more particularly, to a flat panel display with a touch screen.
Modem electronic devices provide an increasing amount of functionality with a decreasing size. By continually integrating more and more capabilities within electronic devices, costs are reduced and reliability increased. Touch screens are frequently used in combination with conventional soft displays such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma displays and electroluminescent displays. The touch screens are manufactured as separate devices and mechanically mated to the viewing surfaces of the displays.
FIG. 1 shows a prior art touch screen 10. The touch screen 10 includes a transparent substrate 12. This substrate 12 is typically rigid, and is usually glass, although sometimes a flexible material, such as plastic, is used. Various additional layers of materials forming touch sensitive elements 14 of the touch screen 10 are formed on top of the substrate 12. The touch sensitive elements 14 include transducers and circuitry that are necessary to detect a touch by an object, in a manner that can be used to compute the location of such a touch. A cable 16 is attached to the circuitry so that various signals may be brought onto or off of the touch screen 10. The cable 16 is connected to an external controller 18. The external controller 18 coordinates the application of various signals to the touch screen 10, and performs calculations based on responses of the touch sensitive elements to touches, in order to extract the (X, Y) coordinates of the touch.
There are three commonly used touch screen technologies that utilize this basic structure: resistive, capacitive, and surface acoustic wave (SAW). For more information on these technologies, see xe2x80x9cWeighing in on touch technology,xe2x80x9d by Scott Smith, published in Control Solutions Magazine, May 2000.
There are three types of resistive touch screens, 4-wire, 5-wire, and 8-wire. The three types share similar structures. FIG. 2a shows a top view of a resistive touch screen 10. FIG. 2b shows a side view of the resistive touch screen 10. The touch sensitive elements 14 of the resistive touch screen 10 includes a lower circuit layer 20; a flexible spacer layer 22 containing a matrix of spacer dots 24; a flexible upper circuit layer 26; and a flexible top protective layer 28. All of these layers are transparent. The lower circuit layer 20 often comprises conductive materials deposited on the substrate 12, forming a circuit pattern.
The main difference between 4-wire, 5-wire, and 8-wire touch screens is the circuit pattern in the lower circuit layer 20 and the upper circuit layer 26, and the means for making resistance measurements. An external controller 18 is connected to the touch screen circuitry via cable 16. Conductors in cable 16 are connected to the circuitry within the lower circuit layer 20 and the upper circuit layer 26. The external controller 18 coordinates the application of voltages to the touch screen circuit elements. When a resistive touch screen is pressed, the pressing object, whether a finger, a stylus, or some other object, deforms the top protective layer 28, the upper circuit layer 26, and the spacer layer 22, forming a conductive path at the point of the touch between the lower circuit layer 20 and the upper circuit layer 26. A voltage is formed in proportion to the relative resistances in the circuit at the point of touch, and is measured by the external controller 18 connected to the other end of the cable 16. The controller 18 then computes the (X, Y) coordinates of the point of touch. For more information on the operation of resistive touch screens, see xe2x80x9cTouch Screen Controller Tips,xe2x80x9d Application Bulletin AB-158, Burr-Brown, Inc. (Tucson, Ariz.), April 2000, pages 1-9.
FIG. 3a shows a top view of a capacitive sensing touch screen 10. FIG. 3b shows a side view of the capacitive sensing touch screen 10. The touch sensitive elements 14 include a transparent metal oxide layer 30 formed on substrate 12. Metal contacts 32, 34, 36, and 38 are located on the metal oxide layer 30 at the comers of the touch screen 10. These metal contacts are connected by circuitry 31 to conductors in cable 16. An external controller 18 causes voltages to be applied to the metal contacts 32, 34, 36, and 38, creating a uniform electric field across the surface of the substrate 12, propagated through the transparent metal oxide layer 30. When a finger or other conductive object touches the touch screen, it capacitively couples with the screen causing a minute amount of current to flow to the point of contact, where the current flow from each comer contact is proportional to the distance from the comer to the point of contact. The controller 18 measures the current flow proportions and computes the (X, Y) coordinates of the point of touch. U.S. Pat. No. 5,650,597, issued Jul. 22, 1997 to Redmayne describes a variation on capacitive touch screen technology utilizing a technique called differential sensing.
FIG. 4a shows a top view of a prior art surface acoustic wave (SAW) touch screen 10. FIG. 4b shows a side view of a SAW touch screen 10. The touch sensitive elements 14 include an arrangement of acoustic transducers 46 and sound wave reflectors 48 formed on the face of substrate 12. The sound wave reflectors 48 are capable of reflecting high frequency sound waves that are transmitted along the substrate surface, and are placed in patterns conducive to proper wave reflection. Four acoustic transducers 46 are formed on the substrate 12 and are used to launch and sense sound waves on the substrate surface. A cable 16 is bonded to the substrate 12, and contains conductors that connect the acoustic transducers 46 to an external controller 18. This external controller 18 applies signals to the acoustic transducers 46, causing high frequency sound waves to be emitted across the substrate 12. When an object touches the touch screen, the sound wave field is disturbed. The transducers 46 detect this disturbance, and external controller 18 uses this information to calculate the (X, Y) coordinate of the touch.
FIG. 5 shows a typical prior art electroluminescent display such as an organic light emitting diode OLED flat panel display 49 of the type shown in U.S. Pat. No. 5,688,551, issued Nov. 18, 1997 to Littman et al. The OLED display includes substrate 50 that provides a mechanical support for the display device. The substrate 50 is typically glass, but other materials, such as plastic, may be used. Light-emitting elements 52 include conductors 54, a hole injection layer 56, an organic light emitter 58, an electron transport layer 60 and a metal cathode layer 62. When a voltage is applied by a voltage source 64 across the light emitting elements 52, via cable 67, light 66 is emitted through the substrate 50, or through a transparent cathode layer 62.
The OLED structure described in relation to FIG. 5 is commonly known as a bottom-emitting structure, where light is emitted through the substrate 50, conductors 54, and hole injection layer 56. An alternative OLED structure, known as a top-emitting structure, similar to that described by International Patent WO 00/17911, issued on Mar. 30, 2000 to Pichler, is shown in FIG. 6. Here, light emitting elements 52, including conductors 54, a hole injection layer 56, an organic light emitter 58, an electron transport layer 60 and a metal cathode layer 62, are formed on substrate 50. A transparent cover sheet 51 is then placed above metal cathode layer 62, and is sealed to the substrate 50. In the top-emitting OLED structure, light is emitted by the organic light emitter 58 through the electron transport layer 60, the metal cathode layer 62, and the transparent cover sheet 51. Less light is absorbed or scattered in top-emitting OLEDs, making the device more efficient. Additionally, top-emitting OLEDs often allow for larger pixel fill factors, since the light emitted is not blocked by conductors 54.
Conventionally, when a touch screen is used with a flat panel display, the touch screen is simply placed over the flat panel display, above the surface from which light is emitted, and the two are held together by a mechanical mounting means such as a frame. FIG. 7 shows such a prior art arrangement with a bottom-emitting touch screen mounted on an OLED flat panel display. After the touch screen and the OLED display are assembled, the two substrates 12 and 50 are placed together in a frame 68. Sometimes, a narrow air gap is added between the substrates 12 and 50 by inserting a spacer 72 to prevent Newton rings. The thickness and materials in the substrates can degrade the quality of the image. When light passes from the underlying flat panel display through the touch screen, a change in refractive index occurs. Some light is refracted, some light is transmitted, and some light is reflected. This reduces the brightness and sharpness of the display.
Although FIG. 7 illustrates a conventional mounting means for a touch screen to a bottom-emitting OLED, the same basic method may be used for mounting a touch screen to a top-emitting OLED. Here, the touch screen""s substrate 12 is placed together with the transparent cover sheet 51 (not shown) in frame 68. A narrow air gap may be placed between the substrate 12 and the transparent cover sheet 51 by inserting spacer 72. Light emitted by the light emitting elements 52 then passes through the transparent cover sheet 51, through the substrate 12, and through the touch sensitive materials 14.
U.S. Pat. No. 5,982,004 issued Nov. 9, 1999, to Sin et al. describes a thin film transistor that may be useful for flat panel display devices and mentions that touch sensors may be integrated into a display panel. However, Sin et al. do not propose a method for doing so.
U.S. Pat. No. 6,028,581 issued Feb. 22, 2000, to Umeya describes a liquid crystal display with an integrated touch screen on the same face of a substrate to reduce parallax error due to the combined thickness of the liquid crystal display and the touch screen. This arrangement has the shortcoming that the existing pixel array layout must be significantly modified, incurring additional cost and reducing pixel fill factor.
U.S. Pat. No. 5,995,172 issued Nov. 30, 1999, to Ikeda et al. discloses a tablet integrated LCD display apparatus wherein a touch sensitive layer is formed on the same side of a substrate as the LCD.
U.S. Pat. No. 5,852,487 issued Dec. 22, 1998, to Fujimori et al. discloses a liquid crystal display having a resistive touch screen. The display includes three substrates.
U.S. Pat. No. 6,177,918 issued Jan. 23, 2001, to Colgan et al. describes a display device having a capacitive touch screen and LCD integrated on the same side of a substrate.
There remains a need for an improved touch screen-flat panel display system that minimizes device weight, removes redundant materials, decreases cost, eliminates special mechanical mounting design, increases reliability, prevents Newton rings, and minimizes the degradation in image quality.
The need is met according to the present invention by providing a touch screen display that includes an electroluminescent display; a touch screen, and a transparent sheet that functions as an element of both the electroluminescent display and the touch screen.
The display according to the present invention is advantageous in that it provides a display having a minimum number of substrates, thereby providing a thin, light, easily manufacturable display.